Circuit-faulting fuse construction



March 28, 1950 PITTMAN 2,501,963

CIRCUIT-FAULTING FUSE CONSTRUCTION File d Aug. 4, 1947 2 Sheets-Sheet 1 INVENTOR March 28, 1950 Filed Aug. 4, 1947 R. R. PITTMAN 7 2,501,963

CIRCUIT-FAULTING FUSE CONSTRUCTION 2 Sheets-Sheet 2 Fig.8

INVENTOR Patented Mar. 28, 1950 UNITED STATES PATENT OFFICE CIRCUIT-FAULTING FUSE CONSTRUCTION Ralph E. Pittman, North Little Rock, Ark.

Application August 4, 1947, Serial No. 765,926

6 Claims. 1

This invention relates generally to fuses for electric circuits, and specifically to a fuse suitable for application to transmission circuits the Voltages of which are too high for satisfactory use of available types of high voltage fuses, such voltages at this time being 161 kv. and higher.

The objects of the invention include (1) the provision of a fuse which will rupture at a predetermined current therethrough, and in response to such rupture will cause only a transient fault on the connected circuit; (2) the provision of a fuse construction particularly applicable to high voltage circuits which are provided with a grounded source in accordance with common practice; (3) a fuse construction embodying corona-proof features both with respect to corona losses and effects of nitrogen acids attending corona; (4) a construction in which a portion of the fuse link moves following the passage of a predetermined current therethrough to effect faulting of the connected circuit and subsequent disconnection of the fuse link and (5) the provision of a simple and inexpensive fuse construction suitable for very high voltage circuits. Other objects will be obvious or pointed out hereinafter.

Because of the present commercial unavailability of high voltage fuses suitable for application to circuit voltages exceeding 138 kv., various schemes have been employed to disconnect a tap circuit from a main transmission circuit in response to an excess current condition in tap circuit. There are only three schemes in common use. The first is an unreliable arrangement, which includes the automatic opening of a motor driven air break switch in response to an excess current through a current transformer in the tap circuit, causing a long are to form on the arcing horns of the switch which may eventually be blown to another phase and thereby fault the circuit. The second is an arrangement for operating a motor driven switch connected between a phase wire and ground, thereby imposing an objectionable permanent fault on the circuit,

The manner in which disconnec-I of an embodiment of the invention; Fig. 2 is a plan view; Fig. 3 is an end view; Fig. 4 is a fragmentary view, partly in section showing the construction of the fuse link embodied in the construction; Fig. 5 is a section of the fuse link taken along the line 55 of Fig. 4; Fig. 6 is another section of the fuse link taken along the line 6-6 of Fig. i; Fig. 7 is a diagrammatic sketch showing an application of the invention to an electric circuit; and Fig. 8 diagrammatically shows a reclosing circuit breaker desirable for use in the circuit to which the invention is applied.

Referring to Figs. 1, 2 and 3 of the drawing, a metal base H], which in common practice in high voltage installations is maintained at ground potential, as by means of the connection to ground indicated symbolically at 35, has mounted thereon a laterally extending metal rod H, the latter being conveniently welded to the base It] near the midpoint thereof. On the base ll, near the respective ends thereof, are mounted, by means of the bolts l4 upwardly extending insulator stacks l2 and I3, the height of the stacks being determined by the voltage-to-ground rating of the device in accordance with common practice.

The metal source terminal i5 is mounted at the top of the stack l2 by means of the bolts 11, extending longitudinally outward to provide means for the connection of a source conductor, and the source fuse link supporting arm l8, of conducting material, is fastened to the top of the stack 12 by means of the bolts 32 in physical con tact with the terminal I5, and extends laterally therefrom on the side of the base from which the rod l I extends. In similiar fashion, the metal load terminal 56 is mounted on the stack I3, and the load fuse link supporting arm l9; of conducting material, is fastened in physical contact with the terminal I6 by the bolts 32, and extends later ally therefrom in substantially parallel relationship with the arm l8.

Under normal conditions, the circuit through the device is completed through the fuse link 22, which spans the space between the respective ends of the arms l8 and I9, being fastened to the arm l8 by the'fuse link terminal 20, and to the arm it by the fuse link terminal 2 I. The fuse link 22, as shown more in detail in Figs. 4, 5 and 6, includes in series circuit arrangement a load end portion 25, a load fusible element 24, an intermediate portion 26, a source fusible element 23, and a source end portion 21. I prefer to use a finely stranded aluminum cable in the construction of the fuselink, forming the fusible elements by cutting out sections of all strands, except those required to form the fusible elements. Aluminum as a metal is substantially unaffected by any nitric acid formed by corona, and the use of a continuous integral strand or strands from end to end including the fusible element avoids the use of solder, which is quickly deteriorated by corona and nitrogen acids. Further, the aluminum conductor provides large diameter with relatively small weight; for example, a 2/0 A. W. G. aluminum conductor made up of 342 strands of 24 A. W. G. wires has a diameter of /178 inch. Also, such stranding enables a wide range of cur-- rent ratings of the fusible elements along with good accuracy.

To avoid breakage of the relatively fragile fusible portions of the fuse link, the insulating tubes 28 and 29 are fitted over the outside of the flexible cable so that the fusible elements 24 and 23 are respectively contained therein, and the tubes of conducting material and 3| tightly fitted over the insulating tubes 28 and 29 respectively. The metal tubes 3!! and 3! completely electro-staticah ly shield the fus ble elements 24 and 23, and thereby prevent formation of corona on these small diameter sections. To assure rupture of the fuse link when the fusible element 23 or the fusible element 24 fuses, the material of the insulating tubes 28 and 29 is preferably of hard fiber, or other material capable of evolving sufficient gas within the confined space in response to the presence of an arc to force the respective d sconnected ends of the fuse link out of the tube in endwise direction.

For the purpose of illustrating an applic tion of the invention to an electric circuit, reference is made to Figs. 7 and 8. Here a portion of a three phase system is diagrammatically shown, the source being represented by the Y-co nected high voltage wi ding 33, the neutral of which, in accordance with common practice, is grounded, as at 34. The numerals 45., 41 and All indicate the main transmission line conductors, which are connected to the source conductors 36, 31 and 38, and the latter connected to the source 3.3 by means of the normally closed or reclosing circuit breaker 43. Three fuses, constructed in accordance with the present invention, are respectively interposed between the source conductor 36 and the load conductor 39, the source conductor 3i and the load conductor 40, and the source conductor 3i! and the load conductor M, and the respective load conductors extend to a transformer 42, to which a load may be connected. Fig. 8 diagrammatically illustrates one pole of a normally closed circuit breaker, in which the closing spring 44 normally maintains the breaker in closed circuit position whenever the current through the opening or overload coil 45 is below a predetermined magnitude.

In Fig. 7, one of the fuses is shown in open circuit position, with the intermediate portion of the fuse link 25 shown. as: having moved from the normal position and resting on the grounded member H. small overload on only one phase conductor which is sufficient to fuse the load fusible element 24, but insufficient to fuse the source fusible element 23. Following the fusing of the load fusible element 24, the fuse link 22 is ruptured at that point, and the intermediate portion 26 pivots around a point near the other end of the fuse. link 22, the portion 26 moving downwardly until the grounded member I I is contacted. The load end portion 25 has sufficient length to act as an arcing horn to prevent arc damage to the fuse link terminal This condition may result from a- 2i. Immediately upon contact of the portion 26 with the member H, as shown by the broken lines of Fig. 1, full line-toground short circuit current is established through the source fusible element 23, causing the latter to fuse, rupturing the fuse link at this point and initiating a transient circuit fault in the form of an are between the source end portion 21' of the fuse link and the member H. Since substantially full line-to-ground fault current flows in this arc, the breaker 43 opens in response to the overcurrent condition, extinguishing the arc and restoring service to any other substation which may be connected along the line.

An important feature of the invention resides in the fact that both the load and source ends of the fuse link terminals are cleared, regardless of the amount of excess current passing through the fuse link. It is only necessary that the excess current equal the predetermined fusing current of the load fusible element 24. If only a single fusible element were used, instead of the construction of the invention then the. unmelted. portions of the fuse link may permanently ground either the, source or load terminals. If the former. the entire. circuit cannot be used; if the latter, a three phase connection is established by grounding one corner of the delta of the high voltage transformer, resulting in low 3 phase voltage on the load side, which may cause serious damage to motors'and other load equipment.

It may be observed that it: is. essential for proper operation that the load fusible element always operate regardless of the magnitude of. fau t current, because fusing of only the source. fusible element results in grounding the circuit through the impedance of the connected transformer, whichv may limit the, current through the load fusible element. to a value below its fusing current. Under certain conditions, a high fault current may fusev both elements almost concurrently, but this situation does not affect. the proper operation of the device.

The foregoing description is intended, to be, illustrative rather than limiting, reference being made to the appended claims to ascertain the scope. of the invention.

I claim:

l. Ina fuse construction, insulating means supporting a source fuse link terminal and a load fuse link terminal, a fuse link fastened at its respective ends to the source and load terminals and electrically connecting said terminals, said fuse link embodying two serially connected longitudinally spaced, fusible elements including a load fusible element disposed adjacent. said load terminal, a source fusible element disposed adjacent said source terminal, and, an intermediate por-' tion extending between said fusible elements, said intermediate. portion being arranged to move from the normal position when one of said fusible elements; fuses, and means rigidly supporting a.

grounded conducting member. in the. path of portion being arranged to move from the normal position when either one of said fusibleelements fuses, and means rigidly supporting a grounded conducting member in the path of movement of said intermediate portion.

3. In a fuse construction, insulating means supporting a source fuse link terminal and a load fuse link terminal, a fuse link fastened at its respective ends to said source terminal and said load terminal and electrically connecting said terminals, said fuse link embodying two longitudinally spaced fusible elements including a load fusible element disposed adjacent said load terminal and a source fusible element disposed adjacent said source terminal, andan intermediate portion extending between said fusible elements, said intermediate portion being arranged to move from the normal position when both of said fusible elements fuse, and means rigidly supporting a grounded conducting member in the path of movement of said intermediate portion.

4. In a fuse construction, insulatingsmeans supporting a source fuse link terminal and load fuse link terminal, a fuse link fastened at its respective ends to said source and load terminals and electrically connecting said terminals, said fuse link embodying two unlike longitudinally spaced fusible elements including a load fusible element disposed adjacent said load terminal and a source fusible element disposed adjacent said source terminal, and an intermediate portion arranged to move from the normal position when both of said fusible elements fuse, and means supporting a grounded conducting memher in the path of movement of said intermediate portion.

5. A high voltage fuse construction for use between a grounded source and a load; comprising a grounded metal base, a. conducting member electrically connected to said base and extending outwardly therefrom, spaced insulators mounted on said base and extending upwardly therefrom, source and load terminals mounted respectively on said spaced insulators, outwardly extending arms of conducting material fastened respectively to each of said insulators in conductive relationship with the source and load terminals respectively, a source fuse link terminal and a load fuse link terminal mounted at the respective outer ends of said arms, and a fuse link extending between said fuse link terminals and over said conducting member in vertically spaced relationship therewith, and arranged to contact said conducting member when released in response to passage of a predetermined current therethrough.

6. A high voltage fuse construction for use between a grounded source and a load; comprising a grounded metal base, a conducting member electrically connected to said base and extending outwardly therefrom, spaced insulators mounted on said base and extending upwardly therefrom, source and load terminals mounted respectively on said spaced insulators, outwardly extending arms fastened to each of said insulators in conductive relationship with the source and load terminals respectively, a source fuse link terminal and a load fuse link terminal mounted at the respective outer ends of said arms, and a fuse link extending between said fuse link terminals and over said conducting member in vertical spaced relationship therewith, said fuse link including a load fusible element located adjacent said load fuse link terminal and a serially related source fusible element located adjacent said source fuse link terminal, said load fusible element being adapted to fuse upon passage of a predetermined current therethrough and to release one end of said fuse link for movement to engagement with said conducting member, and said source fusible element being adapted to remain unfused upon passage of said predetermined current therethrough and to fuse upon passage of a sourceto-ground current which is greater than said predetermined load current.

RALPH R. PITTMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,147,448 Schweitzer July 20, 1915 1,821,761 Lemmon Sept. 1, 1931 

